Who's the best blues harp player.

I place my vote for Walter Horton.

While Toots Thielman may have played some blues at times, I would consider him a jazz artist.

Little Walter haas always been one of my favorites for traditional blues.

Once again, "the best" is an impossible question to ask. I saw Jimmy Z. perform at a small club in Los Angeles in the 80's. There were maybe twenty people in the place, and fifteen had to have been his friends. He blew the doors down. Here's a link to more info:

http://www.eharmonica.net/jimmy_z.htm

I don't know about best, but Charlie Musslewhite is pretty good.

My votes would include those already listed above, and I'd add the following fine harp players to the list:
1. Carey Bell
2. Sonny Boy Williamson (I and II)
3. Slim Harpo
4. Kim Wilson (from Antone's in Austin, TX)
5. Paul deLay
6. William Clarke
7. Jerry Portnoy
8. Howlin' Wolf
9. Junior Wells
10. Jimmy Reed